Bettenou is a god (according to Inga, she is like a deity) with the power to turn people's words into a semblance of reality.

Spoiler

However, it is revealed by Shinjuurou that she is a misbegotten soul of mere words. Her original form is similar to that of a large, white-coloured rabbit with pale eyes and markings on each eye.

(Source: Un-Go Wikia)